I have two pairs of Duck Feet fins, and they great fins. One is an original Spearfisherman, and the other is the Giant UDT model. The latter is more worn, and has gotten more flexible with age. THe Spearfisherman looks like it was when new, and is a great representation of this fin. Even being the "giant" variety, the foot pocket on them will not accommodate a thick wet suit boot. To tell the truth, the Scubapro Jet Fin's biggest advantage is the foot pocket, which was larger and more comfortable than the Duck Foot fin worn right-side up. But I wore them for years upside down, and that made them more comfortable. When wet suit boots were made with soles (instead of the older style "booties" without soles), the Duck Feet would no longer fit for cold water diving.
In answer to Dr. Sam Miller's question about what was worn with the Duck Feet, Swimaster had a boot that was fairly thin, and made to be worn with the Duck Feet. It protected from coral and other rocks, but not from cold. Here are some photos of the Duck Feet fins in use, with the booties. These are both the original and the AMF Voit types, and were taken during our training in 1967 at the US Naval School for Underwater Swimmers in Key West, Florida:
You can see the bootie that was being worn by Harry Krause with the Duck Feet. One of the guys, Bob Cassidy, is wearing the AMF Viking, which he had purchased (Duck Feet were issued fins at the US Naval School for Underwater Swimmers at that time).
Here is the reason the bootie was so nice:
We had to exit onto the coral sand, which was quite course and could cause foot injuries.
Here is a boat exit with the Duck Feet being pretty obvious:
I used the USD Aqualung fins on one required swim, and hated them in 1967 or so. They were stiffer, and gave me foot cramps. So I was pleasantly surprised to pick up a pair off E-Bay, and try them in the pool. The pair I have is not as stiff as what I remember from my USAF days, and comparable to the Duck Feet in my opinion now. More later...
SeaRat